1. Field of the Invention
The invention relates to an apparatus for positioning workpieces in a lathe, wherein individual workpieces are fed into the lathe intermittently. More particularly, the invention relates to automatic feeding of contact lens molds into a lathe collet that positions and secures each mold for finish lathing of a surface of a contact lens formed in the mold.
2. Description of the Prior Art
In a conventional method for making contact lenses, a mold, having one surface conforming to a desired surface of the lens, typically a radius concave surface, is filled with a desired lens polymer. After the lens material cures, the exterior or exposed surface of the polymeric casting is lathed to produce the opposite surface of the contact lens. Typically, the lathing forms the posterior lens surface, adding optical power characteristics to the lens.
The lathing process involves securing the lens mold in a chucking device or collet that fixes the mold in coaxial alignment with the lathe spindle. A cutting tool is then brought into contact with the rotating mold, with the tool arranged and programmed to follow various pathways to achieve the desired finished surface.
The mold must be accurately positioned in the collet to ensure achieving a precisely machined optical surface on the lens. Both collet and mold design are important contributors in achieving satisfactory finished lenses. However, the process of loading the molds into the lathe requires such accuracy and dexterity that, conventionally, loading by hand by the lathe operator is necessary, which hand operation limits productivity of this process.
In Ademovic, U.S. Pat. No. 4,924,739, a method and apparatus for positioning contact lens molds for lathing is disclosed which includes a conically surfaced lens mold that conforms to an inner surface of a collet for fixing the lens mold into position for lathing. In operation, an operator must load the lens mold into the hollow lathe spindle, connect an air line to the spindle which, when actuated, propels the mold into its final position within the collet, with the surface to be machined exposed. After machining, the operator must reverse the operation, employing vacuum to extract the finished lens mold. The difficulty with this apparatus and method is that while the accuracy of positioning the mold and the collet is addressed by the design of the mold and collet, the process requires that an operator must perform a number of manual tasks, which reduces overall productivity of the process.
Schlotfeldt, in U.S. Pat. No. 3,909,982, describes a contact lens polishing apparatus that is provided with an automatic feed system, wherein a chute delivers lens blanks onto a horizontal support, with the lens blanks facing upward. The individual blanks are advanced horizontally by a piston mechanism onto a pedestal which secures the blank in place and elevates it into contact with the polishing tool. The finished lens is pneumatically blown from the pedestal and then discharged from the machine. This machine, while eliminating hand feeding, is somewhat complex with the blanks traveling a rather complex pathway.
It remains desirable in the processing of contact lenses and similar workpieces to improve productivity of a lathing step by providing an automatic feed apparatus for molds or workpieces that insures precision yet eliminates manual operation of the system, by means of a simple, reliable feeding and discharge apparatus, including a collet assembly having an improved design for initial positioning of the molds or workpieces.